The Sky Diamond - Joined wing glider

[RustyMustard]

Hi all, yesterday i got a fresh load of dollar foam, and this morning i decided to build something.

At first i built a Nutball, since it's such an easy build, took about 20 minutes. I flew a few laps around my yard and it flew great, but i still wasn't really feeling it today, so i ducked back in, grabbed a sheet, and decided to try something a bit different.

The Sky Diamond is the result of a few minutes of measuring and scoring.

28" WS
20" Root
4" Tip
2"x 7" Elevons with foam hinges
700mah RX pack, Orange RX, and two 9g servos
4 oz AUW
6.25 CG

This thing is a real floater, it seems to respond to the slightest of air, yet is incredibly stable and solid. It's a flat sheet, no airfoil, and it glides absolutely perfectly when right on CG. It's also not as picky about the CG as most wings. I haven't given it a proper maiden yet, but i tossed it out over my yard and found it's got a great glide. I was able to find a bit of lift off a slight breeze over my mulberry tree and it responded by gaining altitude without pitch change. Since it's flat plate it also seems to penetrate well, and picks up speed nicely if i push the nose over.

This thing is trainer stable, while it responds well, banging the sticks doesn't throw it off. I don't think it'll loop or roll, but it may work out as a great primary trainer.

I also did the surfaces on it without tape, i just used the round part of my needlenose pliers to mash the hinge line down on both sides and make a solid foam hinge.

Building is also a simple affair, it takes less than a single sheet and basically folds together like foam origami. There are only 7 full depth cuts, all straight lines, and 4 half depth score cuts where it's folded.

I'm going to draw up some plans for this thing soon, after this week i get 5 day weekends and 2 day workweek, i'll have plenty of time, and also build a future version with a 64mm EDF as a parkjet. You crafty builders can probably just look at the pic and see exactly how it's done, with a few through cuts and some score cuts at the bends.

 

[FeWolf]

That is cool

 

[RustyMustard]

Thanks, building it is cool, it's like a pop up book, when you glue the wings together up front with dihedral the tail just falls into place.

Here's some plans if anyone wants to try and play with it, put a KFm4 on it and power it up if you want. I'm going to build another as a KFm4 powered by a 64mm EDF, maybe tomorrow.

 

[RAM]

I like that hinge idea, so much easier than trying to cut a bevel.

 

[RustyMustard]

Bevel hinges are silly, fickle, weak things. I don't know why we still even do it.

If you REALLY want the best foam and tape hinge, here it is. The surfaces on this one are so small it doesn't really need it, and i wanted to save weight. On the KFm4 EDF it'll get tape weaves since they'l see more stress in flight.

 

[RAM]

Totally agree on the tape weave hinge. It's a bit difficult the first time you make one but after that it just comes naturally. For my small foam planes I will be switching over to your "mashed" method. Great tip.

 

[TexasTeacher]

Any chance of getting the measurements?

 

[RustyMustard]

Let me see, i made that on the fly last night, i'll look in my cad file and get all the dimensions.

 

[nerdnic]

Bevel hinges are weak? Say what? Reinforced with a little glue they are incredibly strong, easy to make, and don't require special tape.

 

[RustyMustard]

Here we go, for all the "yardstick" builders out there, start measurin', yeeahw!

 

[RustyMustard]

Bevel hinges are weak? Say what? Reinforced with a little glue they are incredibly strong, easy to make, and don't require special tape.

Bevel hinges weaken the foam where it's beveled, and it's an extra step, and you still need good tape. I don't dig the glue reinforcement, i tried it and the hinges ens up stiffer than i like. Tape weave hinges have no friction at all and have went where bevels failed.

Also, on my RM series airfoil models, the bevel disturbs the air and interferes with the function of the TE device that makes the wing work. I've found lots of limitations, and have made foam rain down across the countryside when bevels failed in flight, fluttering to destruction, while my tape weave hinges were the opposite. A snap reversal in a near gale turned one plane to confetti held together by strips of tape. The only part that survived was the tape weave hinge.

When done properly, it's faster than a bevel, holds tighter, and even crates stiffness along the TE where the bevel crates more flex that pulls the tape from the foam. I've tried to futility to get a bevel hinge that's not crap and i've found tape weave superior in every way.

Another reason is because a lot of my builds are from 1" thick foam. Making a 1" bevel in EPS is ridiculous, but with a tape weave hinge, i get a gapless hinge at neutral that's not a readiboard afterthought hacked up and taped on, the hinge itself is in the airfoil at the 1" thick section and as i said, seals right up on the fast, slippery birds.

Tape weave only gets stronger the more you stress it, like those toy "chinese finger traps" that are a woven tube. Put stress on it and the tape is pulled tight down against the foam rather than lifting. They just don't fail and are super easy.

In comparison it feels like bevel hinges are the caveman with a rock way of doing things with penalties in drag and flow disruption where it matters most, at the TE where vortices develop and flow rejoins.

On most parkflyers you won't know the difference, but start pushing hard and you can tel, even if they don't fail, they make drag.

And there's no special tape, i usually use some cheap, no-name brand i buy at circle K for a dollar a roll packing tape. It's thin, not like the 3m or other mane brand, but that's a plus because it's lighter, while still being as strong as it needs to be.

 

[SP0NZ]

Bevel hinges are weak? Say what? Reinforced with a little glue they are incredibly strong, easy to make, and don't require special tape.

Agreed.

 

[nerdnic]

Bevel hinges weaken the foam where it's beveled, and it's an extra step, and you still need good tape. I don't dig the glue reinforcement, i tried it and the hinges ens up stiffer than i like. Tape weave hinges have no friction at all and have went where bevels failed.

Also, on my RM series airfoil models, the bevel disturbs the air and interferes with the function of the TE device that makes the wing work. I've found lots of limitations, and have made foam rain down across the countryside when bevels failed in flight, fluttering to destruction, while my tape weave hinges were the opposite. A snap reversal in a near gale turned one plane to confetti held together by strips of tape. The only part that survived was the tape weave hinge.

When done properly, it's faster than a bevel, holds tighter, and even crates stiffness along the TE where the bevel crates more flex that pulls the tape from the foam. I've tried to futility to get a bevel hinge that's not crap and i've found tape weave superior in every way.

Another reason is because a lot of my builds are from 1" thick foam. Making a 1" bevel in EPS is ridiculous, but with a tape weave hinge, i get a gapless hinge at neutral that's not a readiboard afterthought hacked up and taped on, the hinge itself is in the airfoil at the 1" thick section and as i said, seals right up on the fast, slippery birds.

Tape weave only gets stronger the more you stress it, like those toy "chinese finger traps" that are a woven tube. Put stress on it and the tape is pulled tight down against the foam rather than lifting. They just don't fail and are super easy.

In comparison it feels like bevel hinges are the caveman with a rock way of doing things with penalties in drag and flow disruption where it matters most, at the TE where vortices develop and flow rejoins.

On most parkflyers you won't know the difference, but start pushing hard and you can tel, even if they don't fail, they make drag.

And there's no special tape, i usually use some cheap, no-name brand i buy at circle K for a dollar a roll packing tape. It's thin, not like the 3m or other mane brand, but that's a plus because it's lighter, while still being as strong as it needs to be.

I think tape is fine an all, but in my experience there aren't any of the negatives you're mentioning here surrounding bevel hinges when done right. And I'm not flying parkflyers, I'm literally pushing DTFB to it's limits in 1200g planes going over 120mph.

 

[TEAJR66]

My planes are usually destroyed before the bevel hinge ever becomes an issue. Besides we are talking about DTFB builds and not 1" foam. That's a whole nother animal. And who is worried about reducing the performance of their foam plane. Sounds like brain scientists trying to cure rocket cancer. I think if drag and stress and what ever other performance concerns become an issue, I will be working with different composite materials. I'm not making a foamy to give Burt Rutan a run for his money.

 

[RustyMustard]

I fly a lot of slope, and a clean plane really matters. A few tape wrinkles can absolutely destroy performance when it's blowing, a tiny bit of drag can mean the difference between punching out to the frontside or getting sucked over the ridge. The bevel hinge would be the dirtiest thing on the plane, when it comes to slope, every little bit counts. It'd be like air brakes on many of my planes, thick or thin wing.

If you're not concerned about the drag penalty or the hit in airfoil performance, then bevels work fine, i guess, though every on of mine would peel off, sometimes before i could even get up the hill to fly. Hiking up, a gust around the hill hitting the TE by surprise would tear 'em off. I'm also in a dry, dusty, and high altitude environment, tape don't stick for long, so maybe you guys don't have problems i do from the environment. UV is higher, maybe it's breaking down the foam more quickly. Foam outside for a few days ends up with a uv cooked coating of yellow dust.

But from my personal experience, the whole bevel idea is laughable, and for no benefit. What's better about a bevel? it's a dirtier hinge and more work to make it that way. Work smart, not hard.

 

[TEAJR66]

Would this be a good airframe to use as an introduction to slope soaring?

 

[RAM]

Would this be a good airframe to use as an introduction to slope soaring?

I have one of his RM slopers half built sitting in the basement.

 

[RustyMustard]

Would this be a good airframe to use as an introduction to slope soaring?

It could be, i haven't gotten much slope time with it, but it's stable and seems to respond to lift well. I'll know more in a few days, i should be able to get some more flying in.

It also depends on what you already fly and how well. If you can fly powered planes with decent control then there would be better ways to start sloping. One would be the "Flytrap" by TireTrax over on RcG, a stupid simple build and a great flyer. It's aerobatic, but it's also very stable and controllable without ever feeling squirrelly. If you've got light to medium, steady air over sea cliff, smaller hills or tighter spots, this would be the bird.

At the other end of the spectrum of conditions, one of my 1" thick RM1 birds would be a better choice for big mountain air on medium to heavy days, as the flytrap would get blown off the lift when it's over 20mph. Those are probably the two easiest build options for a cheap plane that will get bashed to bits.

Remember SLOPE is an acronym for Smashed, Lost, Or Pulverized Entirely. The best introduction is building a cheap chevron wing that goes together in less than an hour and shoving some gear in it. The best planes are those that can really survive some smashing, or so light it can't hurt itself, for an intro to slope, depending on conditions.

 

[RustyMustard]

I built a second one, same dimensions with a 40% KFm4 and 64mm EDF. Although i didn't get much testing in before treeing it in a tight field, i found it's ridiculously stable and easy to fly. My EDF build consisted of the same as the plans above, with an EDF unit shoved inside a 24oz foam coffee cup with the bottom cut out and glued to the top of the wing with the center of the fan housing over the CG. I did tape weave hinges since this one is going to see more stress, the pressed foam hinges are great for gliders of a few oz but not on a parkjet.

It's underpowered, i'm flying a 2s pack on a 4s EDF but it's still got plenty of power to fly. On 3s it'd probably go vertical.

But as far as stability, WOW! This thing would be a great primary trainer, it's so solid it feels like a tamed down high wing trainer and for being a plank, it's incredibly pitch stable and easy to balance. It flies with controls i neutral and 6.25" CG perfectly, lands itself if you let it, and with a bit of back stick you can grease it right in. I was so in awe of how great it was flying that i just spaced out and forgot to turn soon enough in a tight windy field. After a gentle treeing I cracked the tail yanking it out of tree because i'm a huge plane crushing doofus, hehe!

I'll post pics later, my camera is dead right now.

The next step is going to be one with a CF2822 swinging a 10" slowfly prop, as well as experimenting with a rudder.